Conventionally, there exists an antenna device that includes: a substrate made of a dielectric material or a magnetic material; a feed element including a feeding terminal and a feed radiation electrode electrically coupled to the feeding terminal; and a plurality of non-feed elements each including a ground terminal and a non-feed radiation electrode electrically coupled to the ground terminal. The feed radiation electrode and the non-feed radiation electrodes are arranged on the surface of the substrate such that the non-feed radiation electrodes extend in the vicinity of the feed radiation electrode.
The feed radiation electrode has a plurality of branched radiation electrodes having the feeding terminal as a common terminal. Also, an impedance matching circuit is provided between the feeding terminal and a signal source (see, for example, Patent Document 1).